1. Field of the Invention
The present invention relates to a hydrodynamic bearing apparatus and a spindle motor having the same.
2. Description of the Related Art
In general, a hydrodynamic bearing apparatus is provided in a small-sized spindle motor used in a recording disk driving device (hard disk drive, HDD) and a lubricating fluid such as oil is filled in a bearing clearance formed between a shaft and a sleeve provided in the hydrodynamic bearing apparatus. Hydrodynamic fluid pressure is formed while the oil filled in the bearing clearance is pumped to rotatably support the shaft.
That is, in general, in the hydrodynamic bearing apparatus, hydrodynamic fluid pressure is generated through a thrust hydrodynamic groove having a spiral shape or a journal hydrodynamic groove having a herringbone shape to achieve stability in motor rotation.
Further, the journal hydrodynamic groove for generating hydrodynamic fluid pressure in a radial direction may be formed in plural as two sets of journal hydrodynamic grooves on the internal surface of the sleeve.
Meanwhile, recent years have seen technological goals of reducing vibrations generated when the spindle motor is driven as well as an increase in the capacity of the recording disk driving device. That is, improvements in the performance of the hydrodynamic bearing apparatus provided in the spindle motor are required in order to drive the recording disk driving device without errors caused by the vibrations generated when the spindle motor is driven.
To this end, the vibrations generated while the motor is driven need to be reduced by extending a gap between the journal hydrodynamic grooves having the herringbone pattern (that is, increasing the length of a bearing span).
However, in order to prevent the lubricating fluid from being dispersed to the outside of the hydrodynamic bearing apparatus, and further, in order to prevent negative pressure from being generated from the inside of the hydrodynamic bearing apparatus, upper and lower parts may be asymmetrical, based on a maximum pressure area.
In addition, in order to allow the lubricating fluid to flow to the lower part of the sleeve in the end, the upper and lower parts are relatively further asymmetric to each other based on a maximum pressure generation area.
As a result, the span length is reduced.
Therefore, the development of the structure of the hydrodynamic bearing apparatus that can reduce the generation of the negative pressure, suppress the dispersion of the lubricating fluid, and increase the span length is required.